Chuck Norcutt wrote:
>Not that it's terribly significant but 3.5 is actually 2/3 stop slower
>than 2.8.
>
You beat me to it! :-)
>1/3 stop is 3.2, 1/2 stop is 3.4.
>
>
Here, my numbers start to disagree with yours., 1/3 stop down from f2.8
as f3.10 and 1/2 stop down as f3.27.
>I'm showing off. :-) Now that I've got a digital read-out for shutter
>speeds, aperture and ISO all in 1/3 stop increments I'm beginning to
>memorize all the intermediate settings. But I did have to calculate the
>1/2 stop increment. Actually, the precise value is 3.43.
>
>
Again, I get the precise value of 3.27. Am I doing something wrong? I
have some tables I set up in a spreadsheet some time ago.
My table must be correct overall, as the f2, 4, 8, etc. come out exact
and all the intermediate full stops are exact multiples of sqrt of 2.
Are my inter-full-stop values off?
I just recalculated and come up with the same numbers. If one stop down
is half the light, that's half the area. Then I assumed 1/2 stop would
be 3/4 of the area, 1/3 stop down would be 2/3, and so on. I then
calculated back from those areas to get diameters. I then divided the
focal length by those diameters. And I got the same f-stop numbers as
before, although with more complex calculations.
Am I off somewhere here? As you said at the beginning, it's not terrible
significant, as the precision of the actual lenses isn't that high. But
I'm curious.
Moose
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